For example, in water supply and sewerage systems, swimming pools, and large-sized baths to be targeted in the water treatment industries, recreation water such as scenic water, ballast water for marine vessels, potable water and juices to be targeted in the foodstuff industries; fluid medicines such as an injection, and liquid or syrup-like oral medicines to be targeted in the pharmaceutical industries, ultraviolet ray irradiation is performed as a measure for killing or inactivating pathogenic microorganisms and the like generated in or mixed into the liquid. In addition, in many foreign countries, irradiation of radioactive rays is also performed. As a device therefor, radiation irradiation devices such as an ultraviolet ray irradiation device and a radioactive ray irradiation device are used.
In such radiation irradiation devices, to understand the dose of radiation with which pathogenic microorganisms to be killed or inactivated have been actually irradiated is very important for designing the structure and formation of the irradiation device or determining the conditions of emitting radiation in such a manner as to kill or inactivate the pathogenic microorganisms and the like to an appropriate level. Thus, various methods have been proposed.
For example, JP 09-503432 A proposes a fluid treatment system equipped with an irradiation chamber having a radiation source towards a fluid to be treated; a radiation intensity measurement means for measuring the intensity of radiation; an exposure time measurement means for measuring a time during which a fluid a to be treated is exposed to radiation in the treatment chamber; and a radiation dose rate measurement means for measuring a dose rate of radiation with which a fluid to be treated has been irradiated based on the radiation intensity and the exposure time measured by the measurement device and the exposure period measurement means. However, in this method, the dose rate of radiation with which a fluid to be treated has been irradiated is merely measured based on the intensity of the radiation and the exposure time, and the dose of radiation with which each fluid very small substance such as pathogenic microorganisms, which flows with the movement of a fluid to be treated, has been irradiated cannot be measured.
Moreover, JP 2004-249207 A proposes an ultraviolet ray irradiation method in inactivation treatment of protozoans. More specifically, in a method of irradiating protozoans such as Cryptosporidium, which exist in water to be treated, with ultraviolet rays for inactivation, the turbidity state of water to be treated is measured; the measured value of this turbidity and the necessary ultraviolet ray dose preset in accordance with the turbidity are comparatively operated to calculate the current value of the ultraviolet ray dose relative to the turbidity; and the current quantity of a current allowed to flow into a ultraviolet ray germicidal lamp is controlled. However, also in this method, it is attempted to control the dose of ultraviolet rays in the inactivation treatment of protozoans by controlling the current value allowed to flow into a ultraviolet ray killing or the like based on the turbidity and the necessary ultraviolet ray dose preset in accordance with the turbidity. The dose of ultraviolet rays with which each protozoa, which flows with the movement of a fluid to be treated, has been irradiated cannot be measured.
Further, Sommer et al., 2004 “UV drinking water disinfection. —Requirement, Testing and Surveillance: Exemplified by the Austrian National Standards M5873-1 and M5873-2. Proc. 2nd Asia Conf. UV Technol. Environ. Appl.” has reported, as a method of evaluating the dose of ultraviolet rays emitted in an ultraviolet ray treatment chamber, a method of adding microorganism such as Bacillus subtilis and MS2 coliphage to water which flows into an ultraviolet treatment chamber, collecting the microorganisms which have passed through the treatment chamber to thereby calculate the inactivation rate and evaluate an average dose of ultraviolet rays with which the microorganisms, which have passed through the inside of the treatment chamber, have been irradiated. In this method using the organism dosimeter, however, the average dose of ultraviolet rays with which the microorganisms, which have passed through the inside of the treatment chamber, have been irradiated, can be measured. However, it is impossible to evaluate the distribution of the ultraviolet ray dose originating from both the distribution of the dose rate of ultraviolet rays in the treatment chamber and the distribution of the ultraviolet ray exposure time of each microorganism generated due to floating properties. There is a problem that there is no choice but to depend on the estimate of complicated computer simulation for the evaluation of the minimum dose in view of worst cases such as a development of short circuit in the treatment chamber.
Further, JP 64-25086 A proposes a radiation dosimeter containing a support having a layer of microcapsules on the surface thereof, in which the microcapsules contain a wall and an internal phase of a solution of a radiochromic dye, and upon exposure to radiation, the radiochromic dye changes the color or shade and density, and describes that the radiation dosimeter is supplied in the form of single sheets or rolls, and is used as a digital-type or analog-type dosimeter in the fields of foodstuff industries and pharmaceutical industries. However, in this method, the microcapsules merely serve as a shell body for holding the solution of radiochromic dye on the support surface, and the radiation dosimeter is supplied in the form of single sheets or rolls. Thus, with respect to the various fluid very small substances which flow in a liquid with the movement of the fluid, the dose distribution of radiation with which each fluid very small substance has been irradiated or which has been absorbed by each fluid very small substance and/or the minimum dose of radiation cannot be measured.    Patent Document 1: JP 09-503432 A    Patent Document 2: JP 2004-249207 A    Patent Document 3: JP 64-25086 A    Non-patent Document 1: Sommer et al., 2004 “UV drinking water disinfection. —Requirement, Testing and Surveillance: Exemplified by the Austrian National Standards M5873-1 and M5873-2. Proc. 2nd Asia Conf. UV Technol. Environ. Appl.”